Optical intensity method to measure the thickness of coatings deposited on substrates

ABSTRACT

Methods and apparatus for measuring a thickness of a coating on an moving object are provided. Light is directed toward the object at a predetermined location on the object such that a portion of the light interacts with the object. A 1D and/or 2D maximum intensities for at least one wavelength channel is captured that is produced by the portion of the light interacting with the object. A measured average intensity of the wavelength channel and/or intensities and their arithmetic derivatives of multi wavelength channel geometries is converted into 1D (averaged) and/or 2D thickness values. Based on these values an acceptability of the coating is evaluated and thickness calculated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit of U.S. Ser. No.16/065,837 filed Jun. 25, 2018 which is a national stage applicationunder 35 U.S.C. § 371 of PCT/US2017/012087 filed Jan. 4, 2017, whichclaims benefit to U.S. Provisional Application No. 62/275,912 filed onJan. 7, 2016, the contents of which are incorporated herein by referencein their entirety for all purposes. This application further claims thebenefit of U.S. Ser. No. 16/065,839, filed Jun. 25, 2018, which is anational stage application under 35 U.S.C. § 371 of PCT/US2017/012086filed Jan. 4, 2017, which claims benefit to U.S. Provisional ApplicationNo. 62/275,905 filed Jan. 7, 2016, the contents of which areincorporated herein by reference in their entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for opticallymeasuring a thickness of a coating deposited on a moving containerduring on-line productions.

BACKGROUND OF THE INVENTION

During a glass container forming process, a metal-oxide coating istypically applied to the exterior of the glass container. Such coatings,which include tin, titanium, or other reactive metallic compounds, ororganometallic compounds, may be employed to protect the glass containerfrom surface damage, such as abrasions and scratches, which result in aloss of tensile strength for the glass container. High tensile strengthin a glass container is desirable, particularly when containers are massproduced, move rapidly in close proximity along high speed conveyorlines, are filled with carbonated beverages, foodstuffs, etc. thatproduce gaseous pressure within the container and are shipped.

The metal-oxide coating is typically applied when the glass containeremerges in a heated, fully shaped condition from a glassware formingmachine that is at the “hot end” of the system. The containers aretransported away from the forming machine by a conveyor. Temperatures inexcess of 400 degrees Centigrade exist at the surface of the glasscontainers, so that when a heat decomposable inorganic metallic, ororganometallic, compound is applied thereto, the compound reactsimmediately and is converted to a metal-oxide coating.

It is desirable for the coating to be periodically inspected during theglass forming process. Current quality inspection procedures typicallyinvolve an offline process. One or more containers are periodicallypulled from the production line, after the container has cooled down toless than about 100 degrees Centigrade (at the “cold end” of thesystem). The thickness of the metal-oxide coating is then measured todetermine whether the thickness is within a thickness tolerance range.If the thickness is outside the tolerance range, additional containersproduced since the last successful inspection must be inspected todetermine when the process drifted out of specification andoff-specification containers may be destroyed. For example, samplecontainers may be inspected every 4 to 8 hours. If there are about 400to 500 bottles being formed per minute (or about 25,000 to about 55,000bottles per hour), a coating deficiency identified after four hours ofproduction may result in a significant loss of inventory. It is alsoimportant to note that the difference between the pass and failthickness value may be as little as 5 CTU, depending on the manufacturerspecification (CTU=coating thickness unit, 1 nm equals approximately3.45 CTU). Therefore, a highly reproducible extra-sensitive technique isneeded for bottle production process.

Various methods exist for detecting defects in objects to be inspected.

U.S. Pat. No. 4,651,568 is directed to a glass bottle inspection methodand apparatus that uses an acoustic wave pulse to detect defects.Acoustic wave distance and defect measurement apparatus are limitedfirst by the effective coupling of the acoustic wave and second by theobject dimensions. The last limitation is directly related to formingwell resolved pulse. This drawback limits acoustic wave detection ofcoating thickness on solid objects to above 0.1 mm, wherever asthickness precision below 5 nm may be required.

WO 2004/065902 is directed to a method and apparatus for contactlessmeasurement of a coating on a substrate such as a bottle, based oncapturing ultraviolet (UV) radiation reflected from the containersurface. This system is limited to the UV region of the spectrum becauseit depends on the absorption properties of glass below about 350 nm,demonstrated by transmission spectrum for transparent flint glass inFIG. 1. For wavelength below 320 nm, glass generally transmits no morethan approximately 10% of incident light. Referring to FIG. 2, for acylindrical glass container multiple reflections are possible: (1) atouter surface of first glass “wall”, which may be coated; (2) at theinner surface of the first “wall”, (3) at the inner surface of theopposite “wall” of the container; and (4) at the outer surface of theopposite “wall” of the glass container. Because of the low transmittancebelow 320 nm, reflections 2-4 will be very weak and may be ignored,allowing consideration of only reflection from the first interface. Butfor wavelengths greater than 320 nm, all four main scattering rays willbe combined in the reflection optics. Only mechanism 1 is directlycorrelated to the thickness of the coating at the 1^(st) interface. Therest contribute to noise level of the measurement system. The noiselevel will be increased because glass containers are not perfectcylinders; in fact, most glass containers can be described by n-polygonsin cross-section, as shown in FIGS. 3A and 3B. This fact complicates theanalysis of the reflected light. Thus, the method described inapplication WO 2004/065902 is limited to UV, where most of the signalsresulting from secondary surfaces can be ignored due to strongabsorption; and would only be truly effective for wavelength near 320 nmor below. Building an optical setup at 320 nm is quite costly andrequires some special optics, detectors and light sources. One otherlimitation of the method is the distance dependence for the measurementdemonstrated by the authors. Under normal production conditions,containers are rarely aligned perfectly at the center of the conveyerbelt. Just the opposite, the bottles may vary by a few inches in eitherdirection perpendicular to the center line, FIG. 4. This inconsistencywill lead to considerable variation in the distance between thecontainer and any measurement device positioned near the conveyor. Thedistance variation will lead to further increase in the noise level thatmust be accounted for by either additional positioning systems orcomplex calibrations in the thickness measurements. In addition, in theclaims of the invention, the authors rely heavily on the out-couplingand coupling of the excitation and reflected beams into optical fibers.We have measured temperatures in excess of 70° C. at the thicknessmeasurement points, making most fiber coupling unusable due to epoxyfailure in the fiber.

U.S. Publication No. 2009039240 is modified technique to measurethickness using UV excitation source and reflected light collected usingan integrating sphere. This approach is costly and is difficult toimplement due to the size of the integrating sphere. Most of theadhesives used in production of reflection surface (PTFE, Spectralon©,etc.) in integrating spheres start failing above 70° C., making itunusable in the Bottle glass plant environment. In addition, integratingspheres are used as a steady state devices due to long persistenttransient responses and measured signal ‘pulsed stretching’ caused bythe multiple diffused reflections. At the same time, typical 600bottles/min glass production plants may require detection times below 5msec. This approach is also expected to be affected by variable distancebetween containers and the measurement system detectors.

U.S. Publication No. 2013/0222575 is directed to a glass bottleinspection apparatus and method that detects a defect on the glassbottle by an imaging process via one or plural illuminating units and atleast one camera.

U.S. Publication No. 2009/0148031 is directed to a surface inspectionapparatus which scans the surface of an inspection object with aninspection light, receives reflection light from the surface andgenerates a two-dimensional image of the object surface based on thereflection light. The apparatus classifies pixels in the two-dimensionalimage into pixels having tones corresponding to defects on the objectsurface and pixels having tones not corresponding to the defects.

U.S. Publication No. 2004/0065841 is directed to a process and apparatusfor testing the coating thickness on a plastic container by shiningultraviolet light through the container to one or more ultravioletsensors and determining the thickness based on the amount of ultravioletlight passed through the container.

U.S. Pat. No. 6,252,237 is directed to a method for measuring thethickness of a coating on a coated surface, using a solid state array oflight-sensitive elements to measure light emitted from a fluorescingcoating composition and measuring the intensity of the coatingcomposition.

U.S. Pat. No. 6,646,752 is directed to a method and apparatus formeasuring thicknesses of ultra-thin gate oxide layers, by using heattreatment and ellipsometry. Ellipsometry is very sensitive technique andrequires high quality layer construction with very little diffused lightscattering component being present in the signal. It also requiresconsiderable time for reflected signal acquisition. Due to specificdefects and irregularities presented on the bottle surface in FIG. 3B,the diffused light component becomes considerable. Therefore, it isunlikely to be used for on-line coating characterization.

U.S. Pat. No. 5,208,645 is directed to a method and apparatus formeasuring the thickness of a coating around a cylindrical object, byirradiating the object with parallel rays of light in a directionperpendicular to the specimen length and measuring the peak levels ofthe light intensity of light refracted from the specimen and receivedvia an image detecting device.

U.S. Pat. No. 5,991,018 is directed to an apparatus for inspecting athickness or deteriorating situation of a coating layer using an imagepickup unit to receive reflected light or transmission light. The imagepickup signal is compared to a reference formula to determine thethickness of the coating. The inspecting apparatus may measure thethickness of the coating layer on the production line. This technique isconfined for the reflection geometry between 30 and 60 degrees. It alsorequires an incident light to be condition in certain way to achieve aperfect illuminant properties. It also relies on the presence of thereference beam. It also is limited to the coatings with thickness above40 nm. For example, the variation of the bi-stimulus values, X and Yrepresent less than 7.3 and 9% change for the containers havingthickness zero and 45 nm, respectively. These small variation are withinerror of measurements due to complex light scattering by the bottledescribed in FIG. 3B.

Currently practiced optical thickness measurement method, most commonlyusing meters supplied by American Glass Research (AGR), providesaccurate measurement of thin coating thicknesses (e.g., less than about20 nm), as well as accurately identifying small changes in coatingthickness, for static bottles at near ambient temperatures (e.g., <100°C.) using a direct contact measurement approach using index matchingfluid. At the same time, accurate determination of the coating thicknessat the “hot end” of the system during the in-line production process isalso highly desirable, for example, to maintain the coating within aspecified tolerance range and to reduce inventory loss.

SUMMARY OF THE INVENTION

The inventors have developed a non-contact technique for measuringcoating thickness on moving objects. Aspects of the technique enableaccurate coating thickness measurements on curved surfaces at relativelylarge distances (e.g., >5 cm) from, for example, a bottle surface to anoptical detector setup. The technique relies on fast detection of bothreflected and transmitted light, recorded from the surface of the movingobject (e.g., moving at <1 m/s). Software identifies the position of abottle on the time frame of a light beam of less than 5 msec. Thetechnique is substantially insensitive to the ambient light normallypresent inside a manufacturing facilities such as glass containerplants. In some instances, the technique enables measurement ofthicknesses of hot objects with surface temperatures of 400-600° C.

An aspect of the present invention may be embodied in an apparatus formeasuring a thickness of a coating on an object. The apparatus includesat least one light source (101) and several detectors. One to measure areflected light (103) and one to measure a transmitted light (104). Forsome of the aspects of the inventions the transmission detector (104)may be omitted. The position of the incident light and detector can bevaried over the bottle height as shown in FIG. 5A. At least one lightsource is configured to direct light (polarized and/or non-polarizedtoward the object at a predetermined location on the object, such that aportion of the light interacts with the object. The detector collectedreflected signal is configured to capture an image having at least onecolor channel in one dimension (1D) or two dimension (2D) produced bythe portion of the light that interacts with the object. The detectorthat is configured to capture transmitted light is a 1D detector. Ameasurement device includes at least one wavelength channel. Thewavelength channel may be detector designed to measure intensityvariations within a narrow wavelength range. For example, a Si fastresponse detector equipped with a narrow passing band filter (405±10 nm)allows to only capture intensity from the 405±10 nm laser light source.The wavelength width of each wavelength channel may vary depending onthe specific implementation of the invention. In an embodiment, a 1Dsignal or 2D image are directly converted into a thickness measurementfor the coatings on a bottle using data averaging strategies that willbe understood by one of skill in the art from the description herein.

Another aspect of the present invention may be embodied in a method ofmeasuring a 2D thickness map of a coating on an object. In thisembodiment 2D mapping refers to the measurements of thickness variationwithin a predetermined surface area. Light is directed toward the objectat a predetermined location on the object such that a portion of thelight interacts with the object. A 2D intensity image, such as generatedby Camera having at least one color channel is captured. This intensityimage is later converted into a thickness map of the coating withinpredefined surface area. This approach allows explicitly accessing 2Dthickness maps of coating on curved surfaces. This approach can alsoinclude using two, three and n wavelength channel detectors to detectlight from the object, such as conventional color cameras (3 channelsetup) and (n-channel, charge coupled device (CCD) spectrometer.

As an optional step, a feed rate of a coating compound for injector(s)of a coating hood may be adjusted based on thickness indications, forexample, by a controller (i.e., automatically) or by user input via auser interface (in conjunction with a controller). In one embodiment, acontroller may be coupled to a measurement device which may include oneor more of at least one light source and a detector. In someembodiments, the controller may control the injection of the coatingcompositions into the coating hood based on thickness measurementresults determined by measurement device. The controller may be aconventional digital signal processor, a logic circuit or amicroprocessor. It will be understood by one of skill in the art fromthe description herein that one or more of the functions of measurementdevice may be implemented in software and may be performed bycontroller.

DESCRIPTION OF THE DRAWINGS

The invention may be understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, various features of the drawing maynot be drawn to scale. On the contrary, the dimensions of the variousfeatures may be arbitrarily expanded or reduced for clarity. Moreover,in the drawing, common numerical references are used to represent likefeatures. Included in the drawing are the following figures:

FIG. 1 is a transmission spectrum for flint (transparent), not coloredglass bottle

FIG. 2 is a drawing schematic illustrating incident light scatteringmechanism at different container surfaces.

FIG. 3A is a perfect container cross-section area.

FIG. 3B is a real life container cross-section area illustratingmulti-faceted polygon like surfaces of a generic glass bottle.

FIG. 4 is a top down view on a glass conveyer which illustrates anexample of variable bottle location along the conveyor.

FIG. 5A is an example of partial schematic of the measurement setup forparallel to normal drawn at the cylindrical surface

FIG. 5B is an example of partial optical setup for measuring thicknessof bottle using small angle light incidence to the normal drawn on thesurface of the cylinder.

FIG. 6 is a global schematic of the optical setup for measuringthickness of coatings on the bottle surface.

FIG. 7A Intensity of all 4 reflections (FIG. 2) as a function of coatingthickness for flint bottle

FIG. 7B Intensity of reflections 1 and 2 (FIG. 2) as a function ofcoating thickness for flint bottle

FIG. 7C Intensity of reflection 1 (FIG. 2) as a function of coatingthickness for flint bottle.

FIG. 8A Measured thickness [CTU] of SnO₂ coating as a function ofdistance between bottle and detector.

FIG. 8B Percentage change [%] of thickness as a function of distancebetween bottle and detector.

FIG. 9 A depicts a graph showing An example of Blue (456 nm) to Green(556 nm) wavelength channel ratio as a function of the coating thicknessas determined by AGR measurement on Amber bottle.

FIG. 9 B depicts a graph showing An example of Green (556 nm) to Red(663 nm) wavelength channel ratio as a function of the coating thicknessas determined by AGR measurement on Amber bottle.

FIG. 10 A depicts a graph showing Distance to the bottle as a functionof the (green plus red)/2 beam size.

FIG. 10 B depicts a graph showing Predicted thickness of the coating asa function of the AGR measured thickness of the coating. Solid lines areshowing ±50, ±10 and ±5% error with respect to the straight line fit todata.

FIG. 11 A depicts a Schematic of the optical setup.

FIG. 11 B depicts a Magnified part of the optical setup diagram (FIG. 11A) focused on the parabolic mirror and the laser light and bottleinteraction area.

FIG. 12 Schematic of laser spot shape modification by application of thevertical slot before (left) and after (right) being reflected off thecylindrical object. The incident light and reflected light beams areshown.

FIG. 13 depicts an Area of the optical setup where reflection 3 and 4blocking occurs.

FIG. 14 depicts a Magnified schematic diagram for the optical systemdesigned to separate reflected beams 1 and 2 from each other after theiris

FIG. 15 depicts An alternative way of blocking the beams 3, 4.

FIG. 16 A is a graph illustrating calculated reflectances for 4wavelength channels centered at 325, 454 (Red), 545 (Green) and 633(Blue) nm wavelengths, respectively, as a function of SnO₂ coatingthickness using circular polarized incident light.

FIG. 16 B Calculated Blue (454 nm) wavelength channel intensity as afunction of coating thickness in CTU for different angles of incidenceusing s-polarized light.

FIG. 17 is a graph illustrating an experimentally determined thicknesscalibration curve for single (Blue) wavelength channel intensity using areflection setup for amber bottles (FIG. 6).

FIG. 18 is a graph illustrating a ratio of blue to red averagedreflected light intensity for amber bottles as a function of SnO₂coating thickness;

FIGS. 19A and 19B are graphs showing Time response of the 0.75-1 m/secmoving bottle. Both reflected and transmitted signals are recorded using‘Black” and ‘Grey’ color schemes.

FIG. 20 Percentage change of laser power as a function of lasertemperature.

FIG. 21 A sample of the trials at the bottle plant showing calculatedcoating thickness for ˜6000 bottles.

DETAILED DESCRIPTION

An exemplary apparatus will be described with reference to theindividual figures. FIG. 5A is a functional block diagram illustratingapparatus 100 for measuring a film thickness of a coating on object 120.Apparatus 100 may include at least one light source 101. The lightsource can be directed at any point along the light of the containerobject as shown in this drawing. A system may be equipped with 1Ddetector. A 1D detector is a flat surface element integrating allincident light intensity within its surface without differentiating ofthe specific light position on the detector surface. Generatedintegrated intensity signal for the transmitted through the containerlight spot is measured behind the object. For reflected light, severalversions of optical geometry can be utilized using detector (103). Insome embodiment of this invention, spatially resolved thickness maps arerequired, a 2D detector (103) is chosen. A 2D detector is a pixelatedsurface detector, which differentiates spot intensities depending ontheir spatial location on the detector surface. This detector cansimultaneously collect up to three different wavelength channels in twodimensions. In another embodiment of this invention one or two 1Ddetectors collecting integrated light intensities are used. Each 1Ddetector possesses significant sensitivity in a narrow wavelength band.Object 120 may be disposed on conveyor belt 122, and may move past lightsource 101 at a predetermined speed. Object 120 may include transparentglass and/or colored glass. Object 120 may include a coating disposedthereon, the film thickness of which may be measured by apparatus 100.

Polarized and/or non-polarized light source(s) 101 may be configured togenerate at least one light beam within visible and/or IR lightspectrum. The light beam(s) from light source(s) 101 may be focusedand/or directed to interact with object 120 via any suitable opticalcomponents (not shown), such as lenses, beam splitters, mirrors, etc. Insome examples, the light beam may be directed from light source(s) 101to pass through object 120, such as measurement light beam usingtransmission detector 104 shown in FIG. 5A. The angle of incidence canvary from perpendicular to bottle surface (zero degree) to up to, forexample, ±20 degrees, as measured from the normal to the cylindricalsurface, FIG. 5B. In some examples, the light beam from light source(s)101 may be configured to be reflected from object 120, such as reflectedlight beam is directed toward detector 103, FIG. 5A-B. Measurement lightbeam 101 may be configured to interact with object 120 at predeterminedmeasurement location by scanning the object 120 surface.

Wavelength intensity channel detector 103 may be configured to capturean image having at least one color channels. In this case a onewavelength channel device may be, but not limited to a detector equippedwith a filter defining the wavelength sensitivity range of the measuredlight or a monochromatic camera, as an example of the 2D detector. Insome cases, it may consist of at least two wavelength sensitivedetectors. In this case reflected light will be separated in differentwavelength channels either using dynamic filters or a series of beamsplitters and/or dichroic mirrors. In some cases this multi wavelengthchannel detector may contain more channels, such as 1D or 2D CCDcameras. In some cases, these multi-wavelength channel detectors may belocated within a single device, such as a color camera, possessing R, Gand B wavelength color channels. In some cases, each of the multiplewavelength channels may be located within separate housing assemblies,such as independent 1D or 2D photo detectors equipped with opticalfilters. Reflected light image may be produced from interaction ofmeasurement light beam with object 120 at predetermined measurementlocations. The color channels may include wavelengths within near UV(315-400 nm), visible (400-700 nm) and/or IR light (>700 nm) spectrum.In one example, the color channels may include three color channels,including red, green and blue color channels. Detector 103 may include,without being limited to, a charge-coupled device (CCD) detector or acomplimentary metal-oxide semiconductor (CMOS) detector. In someexamples, detector 103 may include a monochrome detector having at leasttwo different color filters disposed thereon, to obtain the at least twocolor channels in reflected image. In some examples, detector 103 may beconfigured to simultaneously capture plural images corresponding toplural measurement locations, FIG. 5 A-B. In some examples, two or moredetectors 103 may be used to capture multiple images simultaneously,FIG. 5A.

Aspects of the invention relate to apparatus and methods of measuring athickness of a film coating disposed on an object. The apparatus mayinclude at least one polarized and non-polarized light source, adetector and a measurement device coupled to at least one detector. Thelight source(s) may be configured to direct non-polarized and/orpolarized light toward the object at a predetermined location on theobject such that a portion of the light interacts with the object. Theportion of the light that interacts with the object is referred toherein as interacting light. As used herein, the term portion of thelight includes all of the light or less than all of the light (e.g., apercentage). The detector(s) may be configured to capture intensity ofat least one wavelength color channel. Each wavelength channel issensitive to detect reflected/transmitted light within a narrowwavelength range. A typical example of these wavelength channels are R,G and B color channels with transmittance intensity maxima at 454, 545and 633 nm, respectively. In certain embodiments of this inventions thewavelength channels are equipped with polarizers that may detect s- andp-polarized light signal. In some examples, at least one wavelengthchannel includes an 1D (detector) or 2D (monochromatic) camera. Adetector is equipped with a non-polarized or polarized optical filterthat allows collection of reflected/transmitted light from the coatedobject within a narrow range of wavelengths defined by the properties ofthe optical filter. In some examples a multi wavelength channel detectormay consist of two 1D detectors or a two wavelength channel camerapossessing two selected wavelength ranges, such as R and B as anexample. In some cases, the measurement apparatus includes threewavelength channel detector: 1D detectors and conventional color camerasincluding red, green and blue color channels. The measurement device maydetermine an average light intensities at each channel and distributionof light intensities in the histogram representation for at least onecolor channels. The measurement device may determine at the thickness incase of the 1D detector or a 2D thickness map in case of the 2D camera.These measurements will determine an acceptability of the coating on theobject based on the determined measurements.

Apparatus 100 may be configured as part of a coating application systemhaving at least one injector as well as an add-on to the system attachedto the coating system assembly. For example, light source(s) 101, anddetector(s) 103 and 104 may be positioned within a coating systemdownstream of injectors or immediately after the exit of a coatingsystem. The coating system may be used to apply the protective filmcoating to hot glass containers via injector(s). Coating system 126 mayisolate the glass containers from ambient conditions, and may furnish acontrolled coating operation atmosphere. Coating system may include anexhaust system (not shown) which captures most of the air-entrainedcoating compound not adhering to the containers. The exhaust system mayminimize the opportunity for the coating compound to attack buildingcomponents. Coating system may include components such as blowers,blowing slots and/or suction slots to produce one or more loops ofhigh-velocity air, such that the coating compound is distributed byinjector(s), is entrained within an air stream and appropriatelydirected to object 120 to be coated. A suitable coating system forcontainers is disclosed in Pat. App. No. PCT/US2013/037520, the contentof which is incorporated by reference herein in its entirety.

It is contemplated that apparatus 100 may be configured to connect to aglobal information network, e.g., the Internet, (not shown) such thatthe captured intensity, images, and/or thickness analysis results mayalso be transmitted to a remote location for further processing and/orstorage.

Existing inventions possess high noise during thickness measurements.The present invention uses several novel approaches to reduce noise,provide reflected signal to distance independent technique capable ofoperating in the visible spectrum.

In one of the approaches, the noise is reduced by eliminating strayreflections from the signal. As presented in FIG. 2, four mainreflections result from the interaction of a light beam with atransparent, ‘Flint’ glass container. Out of the four reflections, onlythe first one is related to the thickness of the transparent coatingthat is being determined at the front of the bottle. Reflections, 2 and3 represent noise and reflection 4 is related to the coating thicknesson the opposite bottle side. For the perfect cylindrical objects thesenoise associated reflections can be averaged out. However, due to theimperfect cylindrical structure typically found in glass containers,shown as an object cross-section, FIG. 3B, these noise reflectionscannot be averaged out and play a considerable role defining difficultyin determining thickness of the coating on the bottle. Specifically,reflections 1-4 due to the outside and inside bottle irregularities anddefects are only partially delivered to the detectors. For example,setup presented in FIG. 6 was used to collect light reflected from thecylindrical Flint bottle surface. The collected reflected intensity thatis related to coating thickness, comprising all four reflectedcomponents, was plotted as a function of coating thickness in FIG. 7 A.Intensities of reflected light increased as a function of coatingthickness. However, one observes a considerable level of noise in themeasurements due to the presence of all four reflections. The reflectedintensity dependence relative to coating thickness was fitted to astraight line with R² value of 83.6%.

Second, reflected beam blocking techniques described in the inventionwere introduced. For this setup, reflections 3 and 4 were removed by theoptical setup and a sum of reflections 1 and 2 was measured, FIG. 6.Resulting reflected intensity calibration curve as a function of coatingthickness is shown in FIG. 7B. The noise of the measurements wasdramatically reduced. The reflected intensity dependence was fitted to asecond degree polynomial with R² value of 97.78%. The removal of noiseresulted in considerable improvement in detection of coatings withrelatively close thickness, ±10 CTU.

Third, optical component setup presented in FIG. 6 was modified furtherto eliminate all three noise related reflections, 2-4. The reflectedintensity 1 was plotted as a function of coating thickness (FIG. 7C).The reflected intensity was fitted using second degree polynomial. Thefitting had a quality of fit of R²=98.3%. Considerable reduction in thenoise level readily allowed differentiation between coating thickness ofzero and 10 CTU, 10 and 20 CTU, 20 and 30 CTU and others. This highquality of the fit allows determination of thickness of the coatingwithin ±2-5% over the entire studied range.

Current invention is focused on reducing error in non-contact thicknessmeasurement. This is accomplished by offering a novel optical designsystem for removing the noise related reflections. Out of the fourpotential reflections, only reflection 1 is directly correlated with thetransparent oxide thickness, while reflections 2, 3, and 4 representnoise in the system. The noise reduction method may be accomplishedwithout switching the excitation wavelength into UV spectral region.Most of the current inventions address reduction of noise reflections byminimizing the transmission of the incident light through the bottle(FIG. 1). FIG. 1 indicates that this may be achieved by switching tousing the UV light due to high absorption of this light wavelengthwithin a bottle. For example, see WO 2004/065902 and US No. 2009039240.In addition to obvious complications and safety concerns arising fromusing UV at wavelength at or below 320 nm, the choice of the excitationsources and optical lens are limited and expensive. In addition, thesensitivity of most commercial detectors is generally small atwavelengths as low as 320 nm, which leads to additional noise in thesesystems.

Our invention utilizes a visible wavelength range excitation lightsource. This light source is inexpensive and is easily available frommost of the commercial optics suppliers, for example Thorlabs. Also,most optical elements have anti-reflection coatings with functionalityoptimized to the visible (400-700 nm) range that are designed to reducestray reflection to below 0.5%. Without the anti-reflection or withpoorly designed coatings, such 400-700 nm anti-reflection componentsused in UV at 350±50 nm, the stray reflections increase to over 4%,which is comparable to the reflections from the containers that are tobe measured. The current invention is designed to separate the multiplepossible reflections, FIGS. 7 A-C. Each of the presented techniques isshown for a sake of non-limiting example of an aspect of the fullinvention. In addition, generally past teachings possess distancedependent signal properties, such that when measured reflected intensityis a decreasing function of distance. This property forces pastprocesses to be placed at close proximity (˜5 cm) to the bottle that isprohibited at the actual Bottle glass plant conveyors. The presentinvention allows to obtain distance independent performance of thereflected signal within a broad distance range from 0 to 30 cm from thebottle. In one specific embodiment of this invention, reflectedintensity of the 405 nm laser light was measured as a function ofdistance from the detector to the bottle. The bottle was placed on atranslation stage that allowed to regulate the distance in a setuppresented in FIG. 6. The laser light was fed through the whole in anoff-axis parabolic mirror (focal distance 4-6 inches). This opticalarrangement allows eliminating the “Ghost” signal observed in the pastinventions utilizing the beam splitter setup that led to considerablenoise. Parabolic mirrors are achromatic and, therefore, are not affectedby optical dispersion effects. The off-axis angle of the parabolic lensis 90 degrees that allows for quick and reliable optical alignments.This can be compared to the beam splitter setup (FIG. 5) where reflectedsignal continues to diverge after the beam splitter. The present designand process allow collimation and convergence of the semi-point lightsource using the off-axis parabolic mirror. The reflected light comingfrom the parabolic mirror is collected by a condenser lens (FIG. 6) or asecond parabolic mirror (FIG. 11A). Measured intensity was converted tothickness (CTU) of the SnO₂ coating, FIG. 8 A. Then, it the thicknesswas converted to the percentage thickness change in FIG. 8 B. It can beseen from these figures that in this embodiment of this invention, adistance independent measurement operation range was from 0 to 15 cm,where thickness fluctuation were below 1%. It can be further extended to20 cm, where thickness decreased by 5% between 15 and 20 cm. This isconsiderable improvement versus the ‘Beam Splitter design’, (FIG. 5).

Further physical displacement of the measurement system away, inperpendicular direction, from the conveyer belt may allow to avoidtemperature shocks to the sensitive, optical and electrical elements ofthe setup. It also may help to avoid direct contact of the system withthe bottles when bottles shift their position on the conveyor (FIG. 4).Despite considerable benefits to our optical design and its improvementover previous designs, due to the divergent nature of the reflectedlight beam coming from the cylindrical objects, reflected light fullcollection is limited at above 40 cm.

In another aspect of this invention, a novel design and process allowobtaining distance independent bottle coating thicknesses as well as‘Standard free’ measurement technique. Current static AGR techniquerequires using ‘0’ and ‘27’ coatings Standards to calibrate the voltagereading into coating thicknesses. In this embodiment, arithmeticmanipulation of the wavelength channel intensities, such as, forexample, use of ratios chosen to reduce noise and improvesignal-to-noise ratio and develop a distance independent thicknessmeasurement technique are used. For example, ratios of blue to red,green to red and blue to green wavelength channels may be used formeasuring thickness of the layer coatings. This invention is independentof the bottle type and therefore, does not require calibration and isrelated to the thickness of the coatings. It relies on the optical setupdescribed above, FIGS. 5 A-B and 6. Examples of the measured reflectedintensity ratios are shown in FIGS. 9 A and 9 B for the blue to greenand green to red excitation channels. The excitation light is that for afiber coupled warm white light source in this case. However, it can alsobe any other light source previously described. The wavelength channelsare defined by the R (peak at 663 nm), G (456 nm) and B (peak at 445 nm)signals obtained using a color camera 3-channel 2D detector system. Theindicated ratios increase as a function of thickness, FIG. 9 A-B. Usingdeveloped correlations and setup constructions, such as FIG. 5A or FIG.6, the thickness of the coating is calculated using polynomial algorithmwith good degree of correlation (±10%) for most samples, FIG. 10 B. Notethat whenever as each reflected intensity for each channel is adecreasing function of distance from the bottle to the detector. Theratio of intensities is constant as a function of distance. Inheritednature of 2D detector in this setup was used to determine the distanceof the bottle with respect to the position of the mirror alignmentsystem (FIG. 10 A). This distance is determined by integrating the 2Dimages of the reflected spot light by 2D detector taken duringmeasurements to obtain an image size. With slightly diverging reflectedbeam sizes, the beam size on the detector will correlate with distanceto the bottle. This as-determined distance from the beam splitter to thebottle may be used to further improve the thickness calculations for thebottle coatings as was done in, FIG. 9B.

Example 1

A light source (101) that may be an LED laser light source (404.6 nm)using a special assembly is directed on the surface of a movingcontainer object. In some instances, it can pass through a beam splitteras shown in FIG. 5A at close to 90 degree angle to the surface of thebottle. In some instances, the laser light can be directed at thecontainer surface at small angle of 0 to 15 degrees to the normal drawnat the container surface with, FIG. 5 B. In some instances of thisinvention, a detector measuring transmittance of this light is placedbehind the container, 104. In some instances, redirection and/orcollection optics are used to direct reflected light from the containertowards fast detectors. In some cases, the light of a narrow wavelengthand/or a series of light sources of narrow wavelength are directedthrough a hole in a parabolic mirror alignment/collection system, FIG.6. These light sources may be directed at different angles to the normalof the container surface positioned in front of the light source. Lightreflected from the bottle surface is collected by the mirroralignment/collection system and redirected towards beam-blocking and/orbeam-redirection optics.

One of representative schematic is shown in FIG. 11 A. The laser lightis designed to enter the hole in the parabolic mirror at a small angleto the normal drawn to the bottle surface, FIG. 11 B. To allow thisaction, the hole in the mirror has a conical cross-section. Thisembodiment is not limited by the conical cross-section but also can bedefined by the rectangular cross-section that will allow formation ofthe vertically align light source. The laser light may be modifiedbefore entering a whole in the parabolic mirror. The beam may beconverted into rectangular shape by passing it through a vertical slotand/or a vertically aligned cylindrical mirror (FIG. 11 A and FIG. 12showing beam profiles). A set of horizontal slots placed before theparabolic mirror is design to allow reduction of contribution ofreflections 3 and 4 (FIG. 2) from the opposite wall of the containerbefore the reflected light striking the mirror (FIG. 11 B). Thehorizontal slot converts the beam shape to an extended rectangular shapeand the iris removes stray reflections of the light caused byinteraction of the laser with the hole inside the parabolic mirror, FIG.11. 90 degree off-axis parabolic mirror is aligned to redirect thereflected light from the horizontal plane of the bottle surface towardsthe top of the diagram. All 1, 2, 3 and 4 reflections are emitted by thebottle. After horizontal slots mostly reflections 1 and 2 are presentwith only small contribution from 3 and 4 reflections. Reflection 1 and2 are redirected by the parabolic mirror towards a light redirectionassembly (beam splitter), FIG. 10 A. These assembly allows to sampleas-collected reflected light and compare it with the light where removalof the reflections. For example, the total signal collected after thisbeam splitter (1+2+3+4). After blocking of the reflections, it becomespossible to reconstitute reflection 1 by subtracting reflections 2+3+4from the total. At the top of the diagram there is an iris that allowsalmost full separation of the reflected beams 1-2 and 3-4, FIG. 13.Experimental reflections of the flint bottle presented in FIG. 7 werecollected by the set up described in FIG. 10A, where the reflection1+2+3+4 were collected after beam splitter (FIG. 7 A). Reflections 1 and2 were collected after iris, FIG. 7B. Large improvements of signal tonoise ratio was observed in this example.

After iris a special optical system allows further separations ofreflections 1 and 2 from each other. A schematic block diagram for thisprocess is shown in FIG. 14-15. These separation allows improving thesignal to noise ratio further, FIG. 7 C. When the distance of the 1^(st)parabolic mirror to the bottle is larger than the focusing distance, thereflected beam converges after the mirror, changing its geometry fromellipsoid with a long horizontal axis into a ellipsoid with a longvertical axis. This optical geometric orientation allows to filterreflections 3 and 4 using vertical slots and an iris, FIGS. 14-15.

Example 2

Using setup similar to that described in Example 1 and withoutseparation of multiple reflections, amber bottles having coatingthickness previously measured by standard AGR meter were measured atvariable distance from the optical collection/redirection system and thebottle surface. Correlation of the known AGR coating thickness withthickness measured by non-contact detection system of this invention wascalculated over two different detector-to-bottle distance ranges. Forclose detector distance range (7-32 mm) the correlation had R² value of98.4%. For farther detector distance range (150-185 mm) the correlationbetween the two measurements had R² value of 97.9%. Thus, using currentinvention similar coating thickness measurement results are readilyobtained when detector is up to 20 cm away from bottle as when detectoris nearly in contact with container (<1 cm).

Example 3

Several examples of optically calculated coating thickness based on theaverage intensity of the wavelength channels are presented in FIG. 15 Afor reflected light. The data were generated using custom program basedon Jones matrix formalism and dispersion parameters of SnO₂ coatings onflat soda lime substrates. The thickness of the SnO₂ coatings wereconverted from nanometers into CTU using known conversion relationship(3.45 CTU=1 nm). Four non-polarized wavelength channels are presented inthis figure, having peak intensity at 325, 454, 545 and 663 nm wereconsidered. The width for each channel was selected at 1 nm. It is clearthat based on the dispersion parameters of the tin dioxide coatings, theintensity of the reflected light increases with the increasing thicknessof the coatings, between 0 and 50 CTU. The biggest increased isdemonstrated using a 325 nm wavelength channel. For example, maximum tominimum ratios for 325, B, G and R wavelength channels were 3.7, 1.73,1.38 and 1.24, respectively. These numbers in some cases may represent afigure of merit showing the maximum possible signal ratio for thethickness spread between 0 and 50 CTUs. The higher this number, the lessnoise will affect the instrumental setup.

Example 4

In the next example, polarized light was used. It helped improving thefigure of merit further. In this example, a setup depicted in FIG. 11 Awas used, where the incidence angle of p-polarized was varied from zeroto 70 degrees. Reflected light intensities were correlated with coatingthickness using similar techniques as in Example 1. The p-polarizedlight showed a figure of merit of a factor of 9 for the SnO₂ coatingshaving 0-80 CTU thickness range. P-polarized light provided the highestfigure of merit for reflection from coatings for the incident anglesabove 60 degree (FIG. 16 B).

Example 5

In the next example, the intensity of the Blue (454 nm) channel wasmeasured using Reflection set up shown in FIG. 5 A without reflectedbeam separation. In this experiment, non-polarized (circularlypolarized) light was directed through a beam splitter at zero degreeangle to the surface of an amber bottle with a diameter of 62 mm. Thereflected signal coming from the bottle was directed at 90 degree angleusing the beam splitter to a color 2D camera. Bottles having differentthickness were characterized and thickness calibration curve wasdeveloped. Both theoretical and experimental data agreed well, FIG. 17.In addition to the average intensity measurements for one channel, twowavelength channels were also used. Both Blue and Red (663 nm)wavelength channels were measured on a series of bottles havingdifferent thickness of the coatings. An arithmetic ratio of Blue to Redwas calculated and is plotted in FIG. 18. A linear increase of the ratioas a function of the coating thickness correlated well with theoreticalpredictions, FIG. 16 A, as well as results described in Example 1. Thisexperiment based on the intensity ratios was bottle distanceindependent.

Example 6

Optical prototype described in detail in FIG. 6 (single parabolicmirror) and FIG. 11 A (double parabolic mirror) was manufactured andtested on a single bottle scanning left to right at speed between 0.75-1m/s in front of the detector. These speeds are expected to be comparableto the bottle conveyors traveling at ˜600 bottles/min. Both reflectedand transmitted 405 nm laser light intensities were recorded as afunction of time in FIG. 19. Transmitted laser intensity is used as amonitoring mechanism for the incident laser power when bottle is not infront of the detector. A computer program measured modification in thelaser power and adjusted the calculated thickness of the coating. Thisstep was important due to considerable variations of the temperature ofthe laser measured at the Bottle plant line (FIG. 20). We observed up to35% reduction in laser power when the temperature of the systemincreased from 25 to 76° C. Maximum value of the reflected peakintensity (FIG. 19) corrected for incident laser power (FIG. 20) wereused to recalculate the coating thickness in CTU for a specific bottle.Using this approach, thickness of the SnO₂ coating for Amber bottles wasrecorded on line for the conveyor delivering 630 bottles/min at theactual bottle glass plant. The thickness of over 100,000 bottles wererecorded during the trials. A 6,000 bottle sample of this study is shownin FIG. 21. Some fluctuation of the bottle thickness were observed. Someof the noisy data were removed by observing the peak width of the signal(FIG. 19). Peaks outside a specific width were removed using a computeralgorithm to obtain a tight data points with an average around 35.5±0.5CTU (FIG. 21). In addition to the time-width peak correction, some ofthe stray reflections were removed by setting the maximum peak intensitythreshold value above a maximum value for the bottle with now coating.These approaches help to improve signal to noise ratio for the opticalsystem.

What is claimed is:
 1. An apparatus for measuring a thickness of acoating on an object, the apparatus comprising: at least one lightsource configured to direct light substantially perpendicularly towardthe object at a predetermined location on the object, a portion of thelight interacting with the object; a wavelength detector configured tocapture an intensity signal comprising at least one channel produced bythe portion of the light interacting with the object; and a measurementdevice coupled to the wavelength detector configured to: determineintensities of light of the at least one channel based on an averagemaximum peak intensity captured by each channel of the at least onechannel, wherein, for each channel, the average maximum peak intensityis an average of multiple maxima wavelength channel intensities takenalong a peak of the channel; and determine at least one of the thicknessor an acceptability of the coating on the object based on the determinedintensities, wherein the apparatus is configured to measure thethickness of the coating on the object when the object is positioned atvarious distances from the light source and the wavelength detector, adisplay configured to display at least one of the determined thickness,thickness maps, an indication that the determined thickness isacceptable, or an indication the determined thickness is not acceptable.2. The apparatus of claim 1 further comprising a controller that isconfigured to adjust a feed rate of the coating, which is sprayed by aninjector onto the object, when the determined thickness of the coatingis out of a predetermined thickness range.
 3. A method for measuring athickness of a coating on an object comprising measuring the coatingthickness using the apparatus of claim
 2. 4. The method of claim 3further comprising adjusting a feed rate of the coating, which issprayed by an injector onto the object, when the determined thickness ofthe coating is out of a predetermined thickness range.
 5. The method ofclaim 3 wherein the object is a glass bottle comprising one or morecurved surfaces.
 6. The apparatus of claim 1, wherein the portion of thelight interacting with the object includes at least one of the portionof the light passing through the object or the portion of the lightreflected from the object.
 7. The apparatus of claim 1, furthercomprising: a controller coupled to the light source, the wavelengthdetector, and the measurement device, the controller configured tocontrol the light source, the wavelength detector, and the measurementdevice, such that the measurement device determines a plurality ofrelative wavelength intensities from respective plural one dimensional(1D) or two dimensional (2D) maps corresponding to plural locations onthe object, wherein the measurement device determines the thickness ofthe coating on the object based on the average maximum wavelengthintensities from the plurality of relative wavelength channelintensities, and the plural 1D or 2D intensity maps corresponding to theplural locations are captured sequentially, simultaneously or acombination thereof.
 8. The apparatus of claim 1, wherein the thicknessof the coating on the object is determined based on a predeterminedrelationship between the determined relative maxima wavelength channelintensities and coating thickness.
 9. The apparatus of claim 1, whereinthe light source is configured to transmit within a predeterminedwavelength range including at least one of visible light or infraredlight.
 10. The apparatus of claim 1, wherein the apparatus furthercomprises a coating hood.
 11. The apparatus of claim 1, wherein amaterial of the coating is selected from a group consisting of metaloxides, titanium oxides, tin oxides, and mixtures thereof.
 12. Theapparatus of claim 1, which is configured to be at or substantiallyadjacent to a hot end of a coating system of a glass bottle formingapparatus.
 13. A method for measuring a thickness of a coating on anobject comprising measuring the coating thickness using the apparatus ofclaim
 1. 14. The method of claim 13 comprising the step of measuring a2D thickness of the coating.
 15. The method of claim 13 wherein thethickness measurement occurs at a hot end of a system for coating forglass bottles.